1. Field of the Invention
The present invention relates generally to the field of mechanical fasteners. More specifically, the present invention discloses a fastener or rivet made of a shape memory alloy that will self-deploy when heated above a critical transformation temperature.
2. Statement of the Problem
Conventional riveting (buck and rivet) requires access to both sides of the workpieces. One person holds the rivet in place while a second person deforms the other side of the rivet with an impact device. Conventional riveting results in the workpieces being held together by the two heads of the rivet, without additional compressive loading of the workpieces.
In many situations, it is difficult or impossible to gain adequate access to both sides of the workpieces. In these situations, blind riveting is required. A number of blind rivet designs have been developed in the past. For example, pop rivets are commonly used in installation of suspended ceilings and for joining sheet metal in light-duty applications. However, blind riveting systems for industrial applications are relatively expensive. Blind rivet designs approved by the Department of Defense are typically at least $3 each. The present invention addresses these shortcomings by providing a more cost-effective fastener suitable for blind riveting that will automatically self-deploy when heated.
Examples of a number of different fasteners using shape memory alloys or other materials with memory characteristics are shown in the following prior art references:
______________________________________ Inventor Patent No. Issue Date ______________________________________ Wolfe 2,994,933 Aug. 8, 1961 Otte, et al. 3,740,839 June 26, 1973 Thellmann 3,762,266 Oct. 2, 1973 Gapp, et al. 3,848,389 Nov. 19, 1974 Krumme 4,485,816 Dec. 4, 1984 Jackson, et al. 4,512,699 Apr. 23, 1985 Ignasiak 4,841,100 June 20, 1989 ______________________________________
Wolfe discloses a plastic grommet made of a material (such as vinyl tubing) having memory characteristics activated by heat. However, the structural limitations of plastic tubing and the shape of the grommet render this design suitable only for light-duty applications.
Otte, et al., disclose a connector having two tines. A metallic band made of a shape memory alloy extends around the tines. The band shrinks when heated, thereby applying a compressive force on the tines to grip an object (such as a wire) held between the tines.
Thellmann discloses a bimetal fastener. The bottom portion of the fastener shank is made of a relatively soft metal to permit the fastener to be readily deformed by manual means.
Gapp, et al., disclose another bimetal fastener having a ductile bottom end and a harder titanium alloy shank. The bottom of the fastener is deformed by manual means.
Krumme discloses a surgical staple made of a shape memory alloy.
Jackson, et al., disclose a daze fastener system in which the bottom portion of the fastener has a frusto-conical shape. The workpieces to be joined together have corresponding frusto-conical apertures to accept the fastener. The purpose of this system is to compensate for mismatches in the coefficient of thermal expansion between the materials being joined.
Ignasiak discloses a retainer post having an internal cavity containing a material (such as a shape memory alloy) that expands when heated. Expansion of this material causes radial expansion of the lower end of the retainer post, thereby holding the post in place with respect to the surrounding hole.
3. Solution to the Problem
None of the prior art references discloses a fastener made of a shape memory alloy having the configuration or blind riveting applications described herein.